1. Field of the Invention
This invention relates to vehicle suspension systems and more particularly to a vehicle suspension system for tandem axles using elastomeric springs.
2. Description of the Prior Art
Suspension systems for wheeled vehicles such as trucks and trailers have utilized steel leaf springs or expandable air springs. Tandem suspension systems have conventionally used an elongated beam, pivotably mounted at a central portion to the vehicle body and mounted to an axle at each end thereof. Leaf springs have been used in lieu of and in addition to the elongated beam to cushion the ride. The leaf springs are subject to failure over time and have limited lateral stability. In case of failure, the entire suspension must be removed for replacement of the spring. Therefore, spring replacement is a major repair for a suspension system and can not be accomplished as a practical matter in the field.
Recently, solid rubber or "elastomeric" springs have offered a compromise between the economical leaf springs and the more expensive air springs. The solid rubber suspension systems provide a more stable ride than a leaf spring and also require less space under the body of the vehicle than the leaf spring and air spring assemblies.
However, the solid rubber springs have always been positioned between the axle and chassis of the vehicle so that any vibrations which pass through the rubber spring would be felt in the body of the vehicle. In addition, each axle has to be individually aligned to make sure that the axle is precisely perpendicular to the longitudinal axis of the vehicle. One such suspension is disclosed in U.S. Pat. No. 3,481,623 to Campbell issued on Dec. 2, 1969.
An example of a tandem axle suspension system wherein a walking beam is joined to the frame through shear rubber bodies is disclosed in U.S. Pat. No. 3,817,551 issued to Moore on June 18, 1974. In the Moore system, the axles are joined to the walking beam through rubber bushings. The walking beam is centrally mounted to the chassis through a series of rubber bodies which are in shear stress.